The value of cross-border transmission capacity is increasing across Southeast Europe as widening price differentials highlight the importance of physical electricity flow. Week 25 illustrated this clearly, with significant spreads between regional markets: Türkiye at €16.66/MWh, Greece at €85.50/MWh, Serbia at €85.73/MWh, Bulgaria at €87.58/MWh, Croatia at €102.36/MWh, Romania at €104.84/MWh, Hungary at €109.16/MWh, and Italy at €127.69/MWh. These price gaps represent potential value only when sufficient interconnector capacity is available to physically transfer electricity between markets.
This environment strengthens the case for introducing a cross-border congestion premium indicator as a recurring market metric. Such a measure would go beyond simple price differentials and capture the true economic value of interconnector access between lower- and higher-priced zones. It would incorporate not only the price spread itself, but also available transmission capacity, congestion constraints, losses, nomination requirements and balancing risk, all of which determine whether theoretical arbitrage can be realised in practice.
One of the most important regional corridors is Serbia–Hungary, where a Week 25 spread of €23.43/MWh created clear incentives for cross-border flows. The Bulgaria–Romania corridor also remains highly relevant, reflecting Bulgaria’s relatively cheaper export position and Romania’s increasing price volatility. In the south, the Greece–Bulgaria link plays a key balancing role, while the Croatia–Slovenia–Italy axis is particularly significant given Italy’s persistent position as the region’s main high-price demand sink.
Looking ahead, congestion value is expected to increase during the summer period. Strong solar generation during midday hours can create localized surpluses, while evening demand peaks continue to generate scarcity conditions in other parts of the system. This divergence increases the importance of flexible transmission access, precise scheduling, and effective nomination strategies to capture cross-border value.
For renewable developers, rising congestion risk can lead to lower capture prices in areas behind constrained network nodes, reducing realized revenue even in high-output periods. For traders, congestion introduces additional layers of optionality and arbitrage potential. For industrial consumers, transmission constraints can transmit high regional price levels into domestic procurement costs, even when local supply conditions appear stable.
Although Southeast Europe continues to move toward deeper market integration, progress remains uneven. It is precisely this uneven integration that creates persistent congestion premiums, shaping both trading opportunities and structural price formation across the region.
